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What is Floyd Toole saying about extra amplifier power and headroom?

I've been reading Floyd Toole's "Sound Reproduction The Acoustics and Psychoacoustics of Loudspeakers and Rooms" and came across a passage that I wish he went into further detail about. It has to do with whether having amplifier headroom has any noticeable improvement in sq. He happens to be talking about getting the bass right in small rooms, but in doing so, he also touches on the use of a larger amp for extra headroom: 

Remedies for unacceptable situations typically included spending more money on a loudspeaker with a “better” woofer (without useful technical specifications, that was a lottery of another kind) and a bigger amplifier (for useless headroom ...

It's the last part ("useless headroom") that I'm curious about. I have notoriously hard-to-drive speakers (Magico Mini IIs). Although the recommended amplification is 50w - 200w, in my experience, that's a bit of an underestimation. I'm driving the Minis with a Musical Fidelity M6PRX, which is rated at 230w @ 8ohms. (The Minis are 4ohm.) The combination sounds excellent to my ears at low to moderate listening levels, but I notice a slight compression in the soundstage at higher levels. My listening room, while small, is fairly well treated with DIY panels made from Rockwool, sound-absorbent curtains, and thick carpeting. So I don't think I'm overloading the room. But I have wondered if an amp with far more power than what's suggested (more headroom) would drive the speakers with a little less effort.

Those of you familiar with Toole or with driving speakers with power to spare, what are your experiences? If I went with, say, a pair of monoblocks that drive 600w @ 4ohm, would the extra headroom address the compression I'm hearing at higher levels? Or am I wasting my time and, potentially, funds that would be better spent elsewhere? 

Thanks!  


128x128diamonddupree
diamonddupree's avatar
diamonddupree OP
75 posts
 
Thanks @erik_squires, IMO, all speakers, even floorstanders, could use a subwoofer and I have one in my system, a JL Audio Fathom 110. It has a 900w class D amp and auto room correction. I have the LP freq. on the subwoofer set to 38hz; the Minis go down to 37hz. With the room correction and the LP freq where it is, I feel like I have the sub and satellites integrated pretty well, at least to my ears. I’m using a single sub because I don’t think the room can handle a second one, and after reading Toole, it seems like I have the recommended placement just about right.

Edit: Here's my room:
https://systems.audiogon.com/systems/9016

What do you think the effect would be of adding extra headroom? Or should I be looking more at low noise and low distortion?

Thanks for the links. I’ll read them now.
diamonddupree's avatar
diamonddupree OP
75 posts
 
@mapman very interesting. So what would I do to increase current delivery? I've done a fair amount to treat the room and I feel like my sub is already pretty well integrated. Here's my room:

https://systems.audiogon.com/systems/9016
 
erik_squires
16,472 posts
 
Hi OP:

Yep, this will integrate well, but leaving the mini's to go down to 40 Hz won't really improve your dynamic range.

Lift up the crossover frequency to 80 Hz.
erik_squires
16,472 posts
 
So a couple of things.  If you don't have a high pass filter on your main amp, the speaker and amp will be forced to reproduce the lower octaves, even though you won't hear it.

Not only does this limit dynamic range, but it increases distortion heard from your mains, both harmonic and Doppler.

If you keep your mains at low volumes, this is not a problem, but if your goal is to use the sub to increase bass AND dynamic range, the high pass filter is a must.
atmasphere's avatar
atmasphere
12,012 posts
 
If you're talking Floyd Toole, then expect to hear about a Distributed Bass Array too... but since that is off topic that's all I'm going to say about it.


But that isn't what the problem is with excess power. In a traditional push-pull solid state or tube amplifier, distortion decreases as you decrease power, to a point that is about 3-7% of total power, at which point the distortion goes back up. Below this point you are getting excess noise and distortion if your amplifier power is too high for your application, since most of the time you are only using a tiny amount of total amplifier power.


A different problem you've referred to is compression at high volume. This is a common complaint with lower efficiency loudspeakers, known as 'thermal compression'. Essentially the voice coils heat up in time with powerful bass notes and the like; this prevents the speaker diaphragm  from moving as far as it should. The only way to avoid this if you want the sound pressure is to go with a more efficient speaker, with which there will be less thermal compression.
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